Pulse modulation phasing



March 16, 1954 J. E. BoUGHTwooD PULSE MoDULATIoN PHASING Filed April 17. 1951 5 Sheets-Sheet l JNVENTOR.

J. E. BouGHTwooD TORNEY March 16, 1954 J. E. BOUGHTWOOD PULSE MODULATION PHASING Filed April 17. 1951 5 Sheets-Sheet 2 SQUARE .l2 WAVE 2 SOURCE \A 32K DlvlOER |5\v l A IGKC l DxvlDER B 5l A" IG To PLATES 4 8Kc OlvlOER OF OTHER B 50 DIST'. CHANNELS 4 f OUTPUT Va Vale Vas Vza Vela Vasa Ve t I I u z R R Z` v l v Jr Tr Tr e 5 if j 5 .c a To OTHER SwlTcHmG GRIOS e Flc-3.3 T11-THUI- lil Lil lil i 32KC Div. OUTPUT r+ B I l f l I I I l l lil El EJ IE Qs A B l E F A lKc DN. OUTPUT J C D G H A" A B C D A BKc Dlv. OUTPUT 5.1' E F O H INVENTOR.

J. EBOUGHTWOOD BY ATT RNEY T au NP NT AU HO C KEYING WAVE 5 Sheets-Sheet 3 DIVIDER SIGNAL INPUT TO ALL EIGHT GRIDS 32V@ ls Vu e INVENTOR.

J. E. BoUGl-n'wooo A ToRNEY March 16, 1954 Filed April 17. v.'1951 SIGNAL FROM SENDING DISTRIBUTOR T au Np NT AU HO C March 16, 1954 Filed April 17. 1951 SIGNAL. @mos 30 TO DISTRIBUTOR J. E. BOUGHTWOOD PULSE MODULATION PI-IASING 5 Sheets-Sheet 4 LOW PASS FILTER RADIO RECEIVER INVENToR J. E. BOUGHTWOOD 717, ,wmf

ATT RNEY March 16, 1954 Filed April 17. 1951 ro FIG. o T- J. E. BOUGHTWOOD PULSE MODULATION PHASING 5 Sheets-Sheet 5 /IIS FIG.'7

J. E. BOUGHTWOOD ATTORNEY Patented Mar. 1e, 1954 2,672,517

zie-72,5171,I BQSELMQDHLATIQN PHASING iilalesite, N, Y. assigner te.

AgpiieatiopAprnit, 1951, seriaLNo. zenne` f-.clillll 01.l .17'.9r) 1.; 2 Thespresent inventionlrelatesftospulsemodlllnf Fig. gisasetgf G Ilyes fory explaining the opere tion systems and more;particularlyetwine-.Rh s

Fig, (L shows farllther` arrangement for the thereof. transmitting., and1,1Tf9ilfi1k dstbu'lf @ffl-*fig- "1? In pulse modulation, systems in .liellfllzintelli;v ,a Fig. 5 shows a suitable circuit for the synchrlf'` sence, signals from a,- nlurality-Qff transmit@ noustgeteef, Fig-2 and,

Figs. Gy nd '7 shovi7 in detail the phasing cirmission systemtda likepluralitv 0f leeiyml 'Y cuits.for'.,the,reqelfefsteinlfFig- 13 Referring new', t0 teedreivi'ne'end more Dar,- the .respective ehannelsit `r, 1e,ciessaryfthai fier: 1o ticilarly iQFie- 1@ there Shown ih'blck form 'VA'. nda'receiving station y A rnplitiide modulation system.` `Iri- Ysignals fromV eigght "sending Vvoice frey hannelsare applied, respectively, to input terminalsm: BMCJD, E, F, G and H. Each of the inputr'terrnna Athro'ughH are coupled toa sending distributor I U through respective lov/ pass 'filtersIIA- throughl LI'I-,IKITIOW Dass lter IIA through' III-[fare designed to out oil frequencies above VY'the desiredfvoce frequency intelligence '(igal's. v`"Sending" distributori 0 wi1l bev described morey'fully ihoonection" with Fig. 2. local oscillator vI2 generates al relatively hiyghyfreq'uency control signal which is amplified byqmpler I3,thel01itpl1 lof Which is applied to oasca'deconneted frequency dividers I4, I5', i6 and IJ. Oscillator, il,Y amplifier I3 and frequency dividers I4, L5, flldand I1 may he of any conventional types designed to give relatively stable outputs. 'Suitable frequency divider circuits, will be described in *fcolnnection with Figs. Gand?.

For purposes of illustrationA only, various frequency'valuesvvill loe aSSurled for oscillator I2 andl the' frequency dividers. While these frequenoie's 'Willj'be used in explaining the operation ofthe systeifxi*E it is to be understood that other frequencies could egually7 well be chosen.

Oscillator7A I2 rhay be chosen to provide a 64 kc. volta'e, `While frequency dividers Iii, i5, IS and Il provide, respectively`,32`, 16, s andA 4 lso. voltages. The 4- kc'. output oflf'reque'ncy' divider I'i y A, n is passed through a band pass filter I3 and cornl'tio e i l. f 'I bine'd 'with' th' output of lov/'pass filter IIA. pre f" With 'the freduencyvalues assumed, the highest signal frequency to befpassed. through ilter IIA should-be 'Wellbelovv Alko., 'for instance, in' the I neighborhood of`3.`3 kc. The outputs of frev in gnregr quency dividers I4, I5 and Iiy are applied, in a e apdpende;d drl"a\ving 50 llflfallel to be'des'criloed; l'iereinaffter, to sending deiei with. referees? ,te t

iiviier" disirlileter. .V0"iesliffirleetiifelf Pleelszeegrem @Le eulseamelitrgle Seeding distribute Iii Serres te. sample, ai e the, Y een? eireerateihe.respeetite!Sienalseeelied i@ terminaisA' thoueh ri. irng' epee of distributor I0 is applied to a synchronous gate 2-i and'to monitor I9. Synchronous gate 29, which Will also be described in detail hereinafter, operates under control of a 64 kc. voltage from amplifier I3. The output of synchronous gate 29 is passed through a low pass lter 2l and applied to an ampliier 22. Filter 2| is designed as a low pass lter to provide attenuation for frequencies higher than 64 kc. The output of amplifier 22 is applied to a transmission medium 23. Transmission medium 23 might be a wire line or, as indicated in Fig. 1, a radio link employing a transmitter 24 and a receiver 25.

The output of receiver 25 is applied to an amplier 26, the output of which is passed through a low pass filter 21, similar to filter 2l. rhe output of lter 21 is applied to a pulse shaper 23, some oi the details of which are described in connection with Figs. 6 and 7 and which is fully disclosed in my copending ap-plication Serial N9. 221,470, filed concurrently herewith. Pulse Shaper 28 is coupled to a synchronous gate 29, similar to gate 29. The output of gate 29 is applied to a receiving distributor 39, the operation of which corresponds to the operation of distributor I9.

Receiving distributor 39, the operation of which is synchronized and phased with the operation of sending distributor I9 in a manner to be described hereinaiter, separates the signal samples taken by distributor I9 and applies them to appropriate detector ampliers SIA through 3IH. The outputs oi amplifiers 31A through 3IH are passed through low pass filters 32A through 32H, respectively, and applied to channel output terminals OA through OH, respectively.

The output of pulse Shaper 28 is also applied to a phase control circuit 33, the output of which is, in turn, applied to a crystal lter 39 tuned to 64 kc. The output of filter 34 is amplified in a tuned amplier 35 and applied to a tuned clipper circuit 36. Phase control circuit 33, filter 3d, amplifier 35 and clipper 39 will be described in detai1 in connection with Figs. 6 and 7. The 64 kc. output of clipper 36 is applied to synchronous gate 29 and to a frequency divider 31, which provides a 32 kc. voltage. Frequency dividers 39 and 39, are coupled in cascade with divider 31 to provide, respectively, voltages of 16 and 8 kc. The outputs of dividers 31, 38 and 39 are applied to receiving distributor 39.

A 4 kc. characteristic frequency or phasing signal, which was applied to the output of low pass lter IIA and which should be present in the output of amplifier 3IA, is derived therefrom through a band pass lter 49 coupled to the output of amplier 3IA. Filter 49 should have a very narrow pass band centered about 4 kc. The output of lter 49 is app-lied to a stepper 4I, the operation of which will be described in detail hereinafter in connection with Figs. 6 and 7. Stepper 4I is coupled to frequency divider 31 and to an alarm 42.

When the system of Fig. 1 is properly phased, the input signals to transmitting channels A through H will appear, respectively, in receiving channels OA through OH. Similarly, the 4 kc. phasing signal added to transmitting channel A will be applied to band pass lter 49. 1f, however, the system is not phased, the signals present in the receiving channels will not be the signals from the corresponding transmitting channels. Similarly, the 4 kc. phasing signal will not be present in receiving channel OA and Will not be applied to ilter 49.

Stepper 4I is arranged to cause receiving dis--4 tributor 39 periodically to advance a channel. Within a maximum of seven advances, the 4 kc. phasing signal will appear in channel OA and will, therefore, be applied to iilter 99. When the 4 kc. phasing signal is present in the output of lter 49, it disables stepper 4I so that receiving distributor 39 will operate normally. If for any reason phasing should be lost, stepper 4l will again cause distributor 39 to advance periodically until proper phasing is restored.

Operation of stepper 4I also actuates an alarm 42, which might be a light, buzzer or other indicator, to indicate lack of proper phasing to operating personnel.

Sending distributor I9 is operated by voltages of xed frequency derived from a common oscillator I2. The 64 kc. oscillations from oscillator I2 also operate synchronous gate 29, so that the same 64 kc. oscillations Will be present in the transmitted signal. It is this same 64 kc. oscillation .which is separated from the received signal in receiver station R to operate frequency dividers 31, 38 and 39. Since receiving distributor 39 is operated by the outputs of dividers 31, 38 and 39, receiving distributor 39 will operate at the same rate as sending distributor I9 and will he properly synchronized therewith.

The distributor operation will now be described with reference to Figs. 2 and 3 which illustrate distributor operation for two channels, A and E, of Fig. 1.

A source I2 of a 64 kc. square wave is coupled in cascade with frequency dividers I4, I5 and I6 providing, respectively, square Wave outputs of 32, 16 and 8 kc. Each of dividers I 4, I5 and i6 has two outputs, the two outputs of a given divider being 189 out of phase. The two 32 kc. outputs are denoted Aqi and Be, the 16 kc. outputs are denoted as As and B'fp, and the 8 kc. outputs are denoted Afp and Bd, the 16 kc. outthe distributor is intended to operate on a binary code and since eight channels are to be sampled, a 3 unit code is required to give eight combinations. The output square waves of dividers I4, I5 and I 6 are illustrated in Fig. 3, where the letters A through H designate the portions of the time cycle devoted to each of the eight channels A through H. The period of one cycle of the 8 kc. square Wave is equal to the time required for sampling the intelligence of all eight channels.

The distributor comprises an amplifier tube V for each channel. In Fig. 2, amplier tubes Va and Ve are illustrated, these tubes having their control grids coupled to channels A and E, respectively. The cathodes of amplier tubes Va and Ve are coupled to ground through biasing resistors Ra and Re, respectively. The anodes of amplifier tubes Va and Ve are interconnected by a conductor 59 and coupled to a source of positive potential through a resistor 5I.

Three rkeying tubes are provided for each channel. Keying tubes Va32, Valli and V08 operate in conjunction with tube Va, while keying tubes Ve32, VeI6 and Ve8 operate in conjunction with tube Ve. The cathodes of tubes Va32, Valli and Va are connected to the cathode of tube Va, While the cathodes of tubes Ve32, VeIB vand Ve are connected to the cathode of tube Ve. The anodes of all the keying tubes are connected together and to a source of positive potential. When one of the keying tubes conducts, the voltage drop produced across the cathode biasing resistor of .its associatedlamplier tube is sufficient to cut offthe associatedainplier Only when all three keying tubes fora given channel are rendered non-conductive by "the square Wave outputs will Vthe associated amplifier tube conduct. Thereforetube'Vav will'conduct only when square waves A, `A' and A" are all'negative. An examination of F'ig. 3 shows that this occurs only during the rst half 'cycle of the Au wave. Therefore lthe intelligeneesignal from channel A will be transmitted only during the first one-eighth cycle of the8 ykcgsquare Wave. Similarly, tube Ve will only conduct when square Waves Afp, A and B" are allnegative, which interval corresponds to the iifth oneeighth cycle of the 8 kc. square wave.

The conduction time intervals for each of the eight channels is indicated in Fig. 3by the letters A through H. The grid connections for the associated keying tubes for all eight channels nec-v essary to provide these conduction intervals can readily be determined from Fig. 3 by noting the square Wave outputs'associated with the channel letters. n

Sending distributorv lll comprises eight amplifier tubes similar to tubes Va and Ve, each provided v/ith three keying tubes so connected to frequency dividers I4, I and I6 that the intelligence signal from each channel is applied to synchronous gateV 2l) -for one-eighth of each cycle of the 8 kc. square wave. In other words, the intelligence signal from each channel is sampled V8000- times per second, each sampling lasting approximately 1/34 millisecond. g

The circuit of Fig. 2 could be used for receiving distributorr 3D by applyingthe outputof synchronous gate 29 to the grids of all the amplifier tubes and by deriving the channel output signals from the anodes of the associated amplifier tubes. In thiscase, conductor 5G would-interconnect the control grids of the amplifier tubes rather than the'anodes thereof.

The keying tubes in either the' sending orreceiving distributor could conveniently be replaced by unilateral conductors, such as crystal-rectiiiers, poled so as to pass current through the associated amplifier tube cathode resistorswhen a positive squarewave voltage is appliedthereto. Such a circuit, arranged as a receivingfdistributor, is illustrated in Fig. 4. The circuit ofFig. 4 corresponds to that'of Fig. 2, except that the keying tubes have been replacedk with rectiflers,

the control grids of the distributing tubes-have been interconnected, and the distributing tubes have been individually coupled to the source of operating. potential.

However, before describingthe operation of the receiver in detail, itvvould bewell to note that the signal pulses leaving the sending distributor are not suitable'for transmission. In thel rst instance, the pulses are too Widefso-that transmission ove'r a medium having a restrictedbandwidth'would result in'further broadening and consequent inter-channel crosstalk. Secondly.

the' signal j'pulsesdornot allY have ithesamelfshape and so vvill each be subjectedv toafgdlfferent modification by the transmissionjmedium. In order to obvi'ate these difficulties, the signaijplses are passed througha synchronous gate 20 vvoperated at 64 kc'. The gate serves the 'dual function. of slicing or selecting' a small 'p'ortion'ofeach pulse for transmission 'and'introducing` a'small V6ft kc. component 'into'the signal.

Fig. '5, which illustratesin'detail' synchronous gate 20, comprises twoelectron discharge tub-es V'l and V2. The 'cathodes oftubes'Vi and' V2 are interconnected and coupledV to ground through two series connected resistors and 6l. The `signalfrom"sending distributor Iilfi's applied vto 'the control grid 'of tube Vl', which 'grid' is coupled to ground through. a resistor 62. A 64 kc. keying I'squ'ar'e wave from amplifuar* I3 is "applied to lthe'control gridof tube'VZ through a capaci- 'tor`*63.. A resistor `154"in'tercouples the control grid of tube V2 and the junction of resistors 60 and'l'. The 'anode' of vtube VI' is"couple'dA toda source of positive potential through 'an'anode resistor RI and a variable resistorR.` The' 'anode of tube V2 is connected to the`junction`of'resistors 'R and RI.

The 'amplitude of the 64 kc. keying Wave applied to the controlgrid oftube Vf'is'sufciently large so that, when positive, theV cathode'current of tube V2 Will develop asuiiici'ently large voltagedrop across resistorsand'i tobias'tube VI beyond cut-off. When the 'keying .Wave vis negative;tube V2 is cutoif and tub'eVl yoperates as a normal amplierf Adjustment of the phase of' the keying wave will vary the 'relative v'I'J'os'ition ofthe portion of thesignal'pulse' that is' sliced. Adjustment ofthe. durations of the positive and "negative parts ofthe rkeying Wave will vary the portion of the' 'signal'wavethati's sliced. The plate currents oftubesKVVand'V2 'vvill'- each. contain 64 kc. components. Asthesecomponents vvill'be substantially 180 out'of'p'h'a'se, they 'can vbe subtracted to control the magritudearid phase "ofthe 64 kc. component 'in the output signal..

This'eo'ntrol may be accomplished by varyin'githe 'value of vresistor R.

Referring now to Figs.v 6 andV 7, the output of radiorreceiver 25 is applied to arnr'flifier"tube1 26.. Tubeis arranged as'av grounded grid amplifier' so that the impedance'presented tothetransmission line from receiver 25 may properly be adjusted byv properly selecting the' 'value of a resistor GQ inthe cathode# circuit of tube V2b. The output of amplieri is appliedlto lovvpas's'flter 2l. Filter 21 is preferably'realizedi asa` linear phase characteristic filter.

f .The output of filter 2Tis derivedfrom a` potentiometer 'l0 and applied to the control grid' of an amplifier tube ll. The-output of amplifierV tube H is applied to the control grid of a-tube"2. Tube l2, together Withftube 13 and their associated circuit elements constitute-a pulse Shaper of the typefully disclosed. in my copending -application-referred to hereinbefore. The outputof the pulse Shaper isapplid to the control grid of tube Vl. Tubes'Vl' ar'dV constitute a"syn chroiious gating circuit'of 'the type'describ'ed hereinbefore in connection Witlilig; `"Ilie' 64 kc. square Wave'keying pulses are applied tothe control grid-of tube V2-'tl/1rougha cridu'ctorl'l. The gatingV circuit is preferably adjusted to slice a portion inthe middle offthes'irial pulsesl The output of the'g'ating circuit vis applicato thereontrol grid of an amplifier tube 15 throughvcoupling 7 capacitor ta'.- Tuefampiised outputottubesis is.

appliedto the signaLgridsef-the ampliefftupes of receiving distributor 30 through a coupling capacitor 16.

The cathode of tube 13 is coupled to ground through a pair of series connected potentiometers 11 and 18. Potentiometers 11 and 18, which form part of a shaping network 19, also serve as cathw ode follower impedances for tube 13 to apply the output thereof to the control grid of an amplifier tube 80 through a coupling capacitor 8|. Tube 80 has an output impedance network 82 tuned to a frequency of 64 kc. The output of tube 80 is applied to the control grid of a phase adjuster tube 83 through a coupling capacitor 84. Tube 83 has substantially equal anode and cathode resistors 85 and 86, respectively. The output of tube 83 is derived from both the anode and cathode through a capacitor 81 and a resistor 88, respectively. Since the signal voltages at the anode and cathode are substantially 180 out of phase, adjustment of capacitor 81 will shift the phase of the resultant output applied to the control grid of a driver amplifier tube 89 through a coupling capacitor S.

The output of tube 89 is applied to the control grid of an amplifier tube 90 through a crystal 8|. Crystal 9| acts as a very sharply tuned band pass filter tuned to a frequency of 64 kc. The anode impedance of tube 60 is constituted by a network 92 tuned to 64 kc. The-output of amplifier tube 80 is applied to a control grid 93 of a clipper tube 94 through a coupling capacitor 85. The cathode of tube 84 is coupled to ground through a pair of series connected resistors 96 and 91 and a by-pass capacitor 88. Control grid 93 is coupled to ground through a rectiiier 99 and to the junction of resistors 06 and 91 through a rectifier |00. Rectiiiers 99 and |00 are so poled as to clip both polarities of the 64 kc. signal applied to grid 03. The anode impedance of tube 84 is constituted by a network |0| tuned to 64 L.

kc. The output of tube 94 is applied to the control grid of tube |02 which is operated as an overdriven amplifier to produce a substantially square wave output signal. The anode of tube |02 is connected to a source of positive potential through two series connecte-:l resistors |03 and |04. The anode of tube |02 is also coupled to the control grid of another overdriven amplifier tube |05 through an integrating network |06. The output of tube |05 is given the proper wave shape for serving as the 64 kc. input of the gating circuit by adjusting the clipping action of the overdriven amplifier I05. The output of tube |05 is amplified and inverted by a gate driver tube |08. The anode of tube |08 is coupled to the control grid of tube V2 through a capacitor |01 and conductor 14.

In Fig. '1 there are shown three frequency divider stages 31, 38 and 39 adapted to provide square wave output voltages of 32 kc., 16 kc. and 8 kc., respectively.

Stage 31 comprises two triode discharge systems l0 and I. The grid of system I I0 is connected to the anode of system included within a tube I2 through a network ||3. Similarly, the grid of system is connected to the anode of system I|0 through a network |I4. The cath- .ode of systems I I0 and II| are interconnected and coupled to ground through a biasing resist-or IIS and a by-pass capacitor ||6. The anodes of systems ||0 and ||I are connected, respectively, to the anodes of a dual diode tube ||1. The Acathodes of tube I |1 are interconnected and con- ;nected through a conductor ||8 to the junction of resistors |03 and |04 in the anode circuit of overdriven amplifier tube |02.

The 64 kc. square wave output or tube |02 controls the switching operations of systems ||0 and I|I resulting from their multivibrator connection. Each complete 64 kc. cycle applied to the cathodes of tube I I1 produces a single switching action of systems ||0 and I, so that a half cycle at 32 kc. is produced at output terminals FI. Terminals FI are connected respectively to the junction of resistors I I9 and |20 in the anode circuit of system ||0 and the junction of resistors I2I and |22 in the anode circuit of system I I I.

Stages. 38 and 33 are each connected in the same manner as stage 31, except that the square wavel control input for stage 38 is applied to double diode |23 thereof from the anode circuit of system while the square wave control input for stage 39 is applied to double diode |24 thereof from stage 38, A

The square wave outputs at terminals F2 and F3 are 16 kc. and 8 kc., respectively. Since the voltage to ground at each of the frequency output terminals of the respective pairs FI, F2 and F3 are substantially 180 out of phase with respect to each other, these terminal to ground voltages may be used as the inputs Aqb, Bo, A, Bqi, A" and B" for receiving distributor 30.

The output of detector ampliiier 3|A of Fig. 1, which constitutes the channel A signal, is applied to band pass filter of Fig. 7. Filter 40 is designed to accept substantially solely the 4 kc. phasing signal added to the output of low pass filter IA of Fig. 1.

The output of filter 40 is applied to the control grid of an amplifier tube |25. The output of tube |25 is rectified by a pair of rectifier elements |26 and |21 intercoupling the anode and cathode electrodes of tube |25. The rectied voltage developed across a load resistor |28 is applied as a biasing potential to the control grid of a tube |23 through a resistor |30. When a 4 kc. signal is present in channel A, the bias voltage developed across resistor |28 will cut off tube |29. When no 4 kc. signal is present in channel A, which occurs when the system is not properly phased, tube |29 will be conductive. The bias voltage developed across resistor |28 is also applied,

i through resistor |30 and a conductor |3I, to an alarm circuit responsive to the absence of a voltage on conductor |3I. Lack of phasing will therefore result in an audible or visual indication to operating personnel.

Tube |32 comprises two triode discharge systems |33 and |34 coupled together in free running multivibrator arrangement. The multivibrator may oscillate at any relatively low frequency. In a preferred embodiment of the invention, 100 cycles per second was chosen as the multivibrator frequency.

The cathode of discharge system |34 is coupled to ground through a series network comprising' resistors |35 and |36. The cathode of discharge system |33 is coupled to ground through the discharge path of triode |29. Therefore, if triode |28 is rendered nonconductive by the bias voltage applied thereto, discharge system |33 will have no cathode return and hence will be nonconductive. If discharge system |33 is nonconductive, no multivibrator switching action can occur.

The multivibrator output is taken from the cathode of discharge system |34 which is coupled to the control grid of tube |31. A 64 kc. synchronizing signal is superimposed on the grid The output ofjtube l3'i,.which.comprises the 100'cycle oscillation'is applied'to the cathodes of double diode til through a conductor 140.

When the multivibrator oscillations* are not suppressedby the biasing potential` appliedk toy tube i29`,1i.` e., when the system is not properly phased, the output of. tube vl3'liwi1l provide short pulses to double diode Il'fata frequencyof 10G` cycles. These pulses ywill occur ataslightphase" displacement from the normalllrc. signal appliedto double diodej I Il through conductor l i3.

The 64 kc. present inlthe input of tube I 33 will cause the time lof each pulse to beclosely correlated with the SLi-lic. signal from conductor: l I8. The. pulse provided approximately every 64o cycles of the 64kc. will" cause anadditional operationof frequency divider 3l; As a result, a periodic skipping action is'prcduced'whereby receiving distributor 30; Will effectively "commutatetwo Ychannels in the time normally Vconsumed `for commutating' one channel. Thisabnormal commutation Will occur atta frequency oft 100 cycles, ork everyl .01 second' until proper phasing is achieved. Obviously, phasingvvill be achieved in a maximum of '7 additionalcommutations because,` if the llflrc. signal Vvvere'presentin channel B', '7 additional-commutations -wouldplace itin channelA, cutting 'oii the multivibrator and returning distributor-operation'to normal: If the 4- kc; signal wereV initially -presentfin any of channelsfC through H, a'shorter-time'would be required for phasing -to`occur.

The grid of tube |31 is also coupled'to alarm voltage'conductor I3! so that'tubelill-Will be cut oi when the 4 lac. signalispresent in channel A, thereby preventing any reaction upon frequency divider'l.

It shouldbe remembered that thefreouencies usedin description of the system are givensolely for purposes of illustration; as manyother frequencies and frequency relationships could be employed.

While the invention has'been described ina particular embodiment thereof and inaparticular use, it is not desired that it be limited there-l one of said transmitting channels to form a conbposite'signal, means to vapply lsaid intelligence sigceiving, channel corresponding to said selected transmittingl channel to derive; therefrom said'vv composite' signal and to" separate said phasing. 4signal fromV said composite signal, and means 'to apply said-'separated phasingsignal tosaidcommutation variation means'` thereby toV disable;

said commutation variation means.

2. A multi-channel pulse modulationl system,

comprising an electronic `sending distributor for successively sampling intelligencesignals lying Within a given frequency band'from the transe.-

mitting channels, a `source of ay characteristic free quency signal lying outsidesaid-given frequency band, means to combine saidcharacteristic fre-- quency signal and the intelligence'signal from a.

selectedone of said transmitting channels toform a composite signal, means to apply said intelli gence signals including said composite signal to said sending distributonan electronic receiving distributor for successively applying said samples to the respective receiving channelscorrespondingvto said transmitting channels for substantially equal time intervals'means totnansmit'the successive samples of `said intelligence signals to said receiving distributor, means periodically vto thereof to periodically commutate atleast two ofv said receiving channels vin* one of said timeintervals, band pass lter means coupledto there:

ceiving channel corresponding to said selected' transmitting channel to derive'therefrom said composite signal and toi separate 'saidcharacteristic frequency signal from said ,composite signa1, and meansA to apply said separated ,characteristic frequency signal to saidskipping means therebyV to disable said skipping means.

3. A multiechannel' pulseV modulation system,

comprising an electronic sending Ldistributor forr successively sampling the intelligence signals from the transmitting channels, a.` sourceof'a characteristic frequency signal, meansto combine saidcharacteristicfrequency signal andfthe intelligence signalfrom aiselectedone ofsai'd" tive receiving channels corresponding" tol saidf transmitting channels for substantially equaltime intervals,` ,means to transmit thesuccessivesamples" of `saidintelligence signals to said' receiving.'

distributor, means tof generate periodic skipping pulses g meanst'o applysaidfskipping pulses .to saidf receiving distributor'thereby to cause` said'ireceiv-v ing distributor periodically to commutate at least two of said receivingcl'lannels'in one of'said" time intervals, meanscoupled'to' the receiving nals including said composite signal to said send# ing distributor, an electronic receiving distributorforsuccessively applying said samples tothe respectivev receiving channels at .a predetermined commutation` rate corresponding' to said transmitting channels for substantially equal time intervals, means to transmit'the successive samples of said intelligence signals tovsaid receiving dis-r channelcorrespondingxto said iselectedfftransmitting channelto derive'therefrom` said composite signali and to separatesaid characteristic frequency signalifrom' saidfcompositevsignal; andv means to apply "saidfseparated characteristic frequen'cy signal toxrsaid skipping pulsegenerating means thereby to disablesaid skipping pulse'generating means.l

4'. A multi-channel Ypulse `modulation system, comprising an electronic sendingl distributor forsuccessively sampling thev intelligence' signals;

fromthe transmitting channels, a sourceoffa characteristic frequency signal, 4means to combines'aid characteristic frequency signal and the in-r te'lligence signal from'a selected 'one of said-trans'-l mitting channels to-'f'orma composite` signal,`

means to apply said intelligence signals including said composite signal to said sending distributor, an electronic receiving distributor for successively applying said samples to the respective receiving channels corresponding to said transmitting channels for substantially equal time intervals, means to transmit the successive samples of said intelligence signals to said receiving distributor, multivibrator means for generating periodic skipping pulses, means to apply said skipping pulses to said receiving distributor thereby to cause said receiving distributor periodically to commutate at least two of said receiving channels in one of said time intervals, band pass iilter means coupled to the receiving channel corresponding to said selected transmitting channel to derive therefrom said composite signal and/to separate said characteristic frequeny signal from said composite signal, disabling means coupled to said multivibrator means, and means to apply said separated characteristic frequency signal to said disabling means thereby to disable said multivibrator means.

5. A multichannel pulse modulation system, comprising an electronic sending distributor for successively sampling the intelligence signals from the transmitting channels, a source of a characteristic frequency signal, means to combine said characteristic frequency signal and the intelligence signal from a selected one of said transmitting channels to form a composite signal, means to apply said intelligence signals including said composite signal tosaid sending distributor, an electronic receiving distributor for successively applying said samples to the respective receiving channels at a predetermined commutation rate corresponding to said transmitting channels for substantially equal time intervals, means to transmit the successive samples of said intelligence signals to said receiving distributor, commutation varying means to cause said predetermined commutation rate to skip at a periodic rate thereby to commutate at least two of said receiving channels in one of said time intervals, means coupled to the receiving channel corresponding to said selected transmitting channel to derive therefrom said composite signal and to separate said characteristic frequency signal from said composite signal, means to apply said separated characteristic frequency signal to said commutation varying means thereby to disable said commutation varying means, and alarm means coupled to said advancing means and responsive to the absence of said characteristic frequency signal in said receiving channel corresponding to said selected transmitting channel to produce an alarm indication When said sending and receiving distributors are not properly phased.

6. In a multichannel pulse modulation system, a phased receiver arrangement comprising an electronic receiving distributor for successively applying at a predetermined commutation rate samples of a received signal to the receiving channels of said system for substantially equal time intervals, said received signal comprising a plurality of intelligence signals each intended for a respective one of said receiving channels and a phasing signal added to a selected one of said intelligence signals, multivibrator means arranged to periodically to cause said receiving distributor to skip thereby to commutate at least two of said receiving channels in one of said time intervals, disabling means responsive to said phasing signal for disabling said multivibrator means, means i2 coupled to the receiving channel corresponding to said selected intelligence signal to derive therefrom said phasing signal, and means to apply said phasing signalto said disabling means thereby to suppress said periodic skipping of said receiving distributor.

7. In a multichannel pulse modulation system, a phased receiver arrangement comprising an electronic receiving distributor for successively applying samples of a received signal to the receiving channels of said system for substantially equal time intervals, said received signal comprising a plurality of intelligence signals each intended for a respective one of said receiving channels and a characteristic frequency signal added to a selected one of said intelligence signals, means periodically to advance said receiving distributor thereby to commutate at least two oi said receiving channels in one of said time intervals, said advancing means comprising a pair of electron discharge systems coupled together in free running multivibrator arrangement and arranged periodically to supply stepping pulses to said receiving distributor, means comprising a third normally conductive electron discharge system interposed in the cathode circuit of one of said pair of discharge systems for disabling said advancing means, means coupled to the receiving channel corresponding to said selected intelligence signal to derive therefrom said characteristic frequency signal, and means to apply said characteristic frequency signal to said third electron discharge system in a sense to render said third discharge system nonconductive thereby to suppress said periodic advancing of said receiving distributor.

8. In a multichannel pulse modulation system, a phased receiver arrangement comprising an electronic receiving distributor for successively applying samples of a received signal to the receiving channels of said system for substantially equal time intervals, said received signal comprising a plurality of intelligence signals lying Within a given frequency range and each intended for a respective one of said receiving channels and a characteristic frequency signal lying outside said given range and added to a selected one of said intelligence signals, means periodically to advance said receiving distributor thereby to commutate at least two of said receiving channels in one of said time intervals, said advancing means comprising a pair of electron discharge systems coupled together in free running multivibrator circuit arrangement and arranged periodically to supply stepping pulses to said receiving distributor, means comprising a third normally conductive electron discharge system interposed in the cathode circuit of one of said pair of discharge systems for disabling said advancing means, band pass filter means coupled to the receiving channel corresponding to said selected intelligence signal to derive therefrom said characteristic frequency signal, and means comprising a rectier circuit coupled to said band pass nlter to apply said characteristic frequency signal to said third discharge system in a sense to render said third discharge system non-conductive thereby to suppress said periodic advancing of said receiving distributor.

= 9. In a multichannel pulse modulation system,

a. DhaSed IBCBVBI arrangement Comprising an electronic vreceiving Vdistributor for successively applying samples of a received signal to the receiving channels of said system for substantially equal time intervals, said received signal comi3 prising a plurality of intelligence signals each intended for a respective one of said receiving channels and a characteristic frequency signal added to a selected one of said intelligence signals, means periodically to cause said receiving distributor to skip thereby to commutate at least two `of said receiving channels in one of said time intervals, disabling means responsive to said characteristic frequency signal for disabling said periodic skipping means, means coupled to the receiving channel corresponding to said selected intelligence signal to derive therefrom said characteristic frequency signal, means to apply said characteristic frequency signal to said disabling means thereby to suppress said periodic skipping of said receiving distributor, and means respon- 14 sive to the absence of said characteristic frequency signal in the receiving channel corresponding to said selected intelligence signal to provide an alarm indication when said receiving distributor is not properly phased with respect to said intelligence signals.

JOHN E. BOUGHTWOOD.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,418,116 Grieg Apr. 1, 1947 2,490,039 Ear-ep Dec. 6, 1949 2,527,638 Keer Oct. 31, 1950 2,527,650 Peterson Oct. 31, 1950 

